In this study, carbon nano-fibers (CNFs) were used to increase the compressive properties of poly(arylene ether sulfone) (PAES) foams. The polymer composite pellets were produced by melt blending the PAES resin with CNFs in a single screw extruder. The pellets were saturated and foamed with water and CO2 in a one-step batch process method. Dynamic mechanical thermal analysis (DMTA) was used to determine the reduced glass transition temperature (T-g) of the CNF-PAES as a result of plasticization with water and CO2. Sharp transitions were observed as peaks in the tan delta leading to accurate quantitative values for the T-g. By accurately determining the reduced T-g, the foaming temperature could be chosen to control the foam morphology. Foams were produced which ranged in density from 290 to 1100 kg/m(3). The foams had cell nucleation densities between 10(9) and 10(10) cells/cm(3), two orders of magnitude higher than unreinforced PAES foam, suggesting that the CNFs acted as heterogeneous nucleating agents. The CNF-PAES foam exhibited improved compressive properties compared to unreinforced PAES foam produced from a similar method. Both the specific compressive modulus and strength increased by over 1.5 times that of unreinforced PAES foam. The specific compressive strength of 59 MPa for the CNF-PAES foam is similar to that of commonly used high performance structural foam, poly(methacrylimide foam). (c) 2009 Elsevier Ltd. All rights reserved.